Hillary Clinton cancelled her appearance at an upcoming event where Democratic presidential candidate Tulsi Gabbard is set to speak.

Clinton was set to give a talk at the 2019 Fortune Most Powerful Women Summit, but subsequently claimed a “scheduling conflict” would prevent her from doing so.

A source close to Clinton told Slate that Hillary dropped out because Kirstjen Nielsen, the former secretary of Homeland Security, is also scheduled to speak at the event.

However, some speculate that the real reason Hillary got cold feet is because Tulsi Gabbard will be attending.

Last week, Clinton claimed that Russia was “grooming” a female Democratic candidate to be a spoiler, clearly referring to Gabbard.

“I think they’ve got their eye on somebody who is currently in the Democratic primary and are grooming her to be the third-party candidate,” said Clinton, adding, “She’s the favorite of the Russians. They have a bunch of sites and bots and other ways of supporting her so far.”

Gabbard hit back with vehemence, tweeting that Clinton represented, “the queen of warmongers, embodiment of corruption, and personification of the rot that has sickened the Democratic Party for so long.”

The former Iraq veteran then released a video in which she asserted, “If you stand up to the rich and powerful elite and the war machine, they will destroy you and discredit your message,” adding that she had suffered smears “from day one of this campaign.”

Hillary & her gang of rich, powerful elite are going after me to send a msg to YOU: “Shut up, toe the line, or be destroyed.” But we, the people, will NOT be silenced. Join me in taking our Democratic Party back & leading a govt of, by & for the people! https://t.co/TOcAOPrxyepic.twitter.com/TahfE2XOek